1. Field of the Invention
The present invention generally relates to a broadband communication system and more particularly to an intermediate frequency local generating circuit for generating an intermediate frequency local signal used in a broadband portable radio phone.
2. Description of the Related Art
Generally, a communication system using a multi-carrier receiving end converts a received radio frequency(RF) signal into a plurality of intermediate frequency signal. This system is based on an orthogonal frequency division multiplexing technique, and can overcome fading effects since symbol periods of the respective channels are lengthened. FIG. 1 is a block diagram illustrating a portion of the receiving end of a typical portable radio phone.
Referring to FIG. 1, in a multi-carrier communication system using N carriers, a radio frequency (RF) signal carried by the respective carrier is processed by a RF processing unit 1. A RF local generator 2 is provided in the receiving end of the terminal to convert the RF signal output from the RF processing unit 1. The RF signal output from the RF processing unit 1 and a RF local signal provided from the RF local generator 2 are mixed together to generate N intermediate frequency (IF) signals.
The N number of IF signals are processed by an IF processing unit 4, and these IF signals are then converted to baseband signals by first and second downward processing of the frequency. Particularly, to generate the N baseband signals from the N number of IF signals, the receiving end is provided with N IF local generators 5 which provide corresponding IF local signals through N paths. The IF signals output from the IF processing unit 4 and the IF local signals from the respective IF local generators 5 are mixed together to generate the baseband signals. Finally, the generated baseband signals are input to a baseband processing unlit for further processing.
As described above, the receiving end of the broadband portable radio phone using N carriers must employ a plurality of IF local generators equivalent to the number of the carriers, which increases the number of required components and increases the manufacturing cost of the circuit. Also, since a plurality of the local generators is required, the size of the circuit is increases which may cause unnecessary noise signals due to the increase of signal lines for connecting the local generators.
Accordingly, an object of the present invention is to solve at least the problems and disadvantages of the related art.
An object of the present invention is to simplify the circuit for the broadband portable radio phone using N carriers.
Another object of the present invention is to provide an intermediate frequency local generating circuit with one intermediate frequency phase locked loop to convert the intermediate frequency signals to the baseband signals.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.
To achieve the objects and in accordance with the purposes of the invention, as embodied and broadly described herein, the intermediate frequency local generating circuit includes an intermediate frequency phase locked loop for feeding back one of the plurality (N) of intermediate frequency local signals, comparing a frequency of the fed-back intermediate frequency local signal with a reference frequency of a portable radio phone, and outputting a pulse signal as a result of comparison; a loop filter for converting the pulse signal output from the intermediate frequency phase locked loop into a DC voltage; a plurality (N) of resonance circuits for receiving the DC voltage output from the loop filter, and outputting different resonance frequencies in accordance with values of their internal elements; and a plurality (N) of intermediate frequency voltage controlled oscillators for receiving the resonance frequencies from the plurality of resonance circuits, and producing the corresponding intermediate frequency local signals in accordance with the resonance frequencies inputted thereto.
The intermediate frequency local generating circuit includes a counter for dividing the frequency of the fed-back intermediate frequency local signal; and a phase comparator for comparing a phase of the frequency divided by the counter with that of the reference frequency. Also, the phase comparator outputs a phase difference signal as a result of phase comparison, and the intermediate frequency phase locked loop outputs the pulse signal having a pulse width corresponding to the phase difference.